import java.util.Scanner;
import java.io.*;
import java.math.*;
import java.util.*;
public class Main {

    //调和平均
    public  static void main(String[] args){
        Scanner in = new Scanner(System.in);

        int n = in.nextInt();
        double[] nums = new double[n];
        double[] numss = new double[n];
        double sum = 0.0;
        for(int i = 0;i<n;i++){
            nums[i] = in.nextDouble();
            numss[i] = 1/nums[i];
            //System.out.println(numss[i]);
            sum+=numss[i];
        }
        double pjsum = sum/n;
        double pjsums = 1/pjsum;
        System.out.printf("%.2f",pjsums);
    }


    //胎压检测
    public static void main4(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int[] pressures = new int[4];
        for (int i = 0; i < 4; i++) {
            pressures[i] = scanner.nextInt();
        }
        int minPress = scanner.nextInt();
        int threshold = scanner.nextInt();

        int max = getMax(pressures);
        boolean allNormal = true;

        // 检查是否所有胎压都符合正常条件
        for (int p : pressures) {
            if (p < minPress || Math.abs(p - max) > threshold) {
                allNormal = false;
                break;
            }
        }

        if (allNormal) {
            System.out.println("Normal");
        } else {
            List<Integer> problemTires = new ArrayList<>();
            for (int i = 0; i < pressures.length; i++) {
                int p = pressures[i];
                if (p < minPress || Math.abs(p - max) > threshold) {
                    problemTires.add(i + 1); // 转换为1-based编号
                }
            }

            if (problemTires.size() == 1) {
                System.out.println("Warning: please check #" + problemTires.get(0) + "!");
            } else {
                System.out.println("Warning: please check all the tires!");
            }
        }
    }

    private static int getMax(int[] arr) {
        int max = arr[0];
        for (int num : arr) {
            if (num > max) {
                max = num;
            }
        }
        return max;
    }


    //吃火锅
    public  static void main3(String[] args){
        Scanner in = new Scanner(System.in);

        String n;
        int[] a = new int[100];
        int count1 = 0;
        int count = 0;
        while(true){
            n = in.nextLine();
            if(n.equals(".")) break;
            count1++;
            Boolean type1 = n.contains("chi1 huo3 guo1");
            if(type1 == true){
                a[count] = count1;
                count++;
            }
        }
        if(count>0){
            System.out.println(count1);
            System.out.print(a[0] + " ");
            System.out.println(count);
        }else{
            System.out.println(count1);
            System.out.println("-_-#");
        }
    }


    //前世档案
        public static void main2(String[] args)
        {
            int n = sc.nextInt();
            int m = sc.nextInt();
            while (m-- > 0)
            {
                String str = sc.next().replace("y", "0").replace("n", "1");
                out.println(Integer.valueOf(str, 2) + 1);//将str从二进制转为int类型
            }

            out.flush();
            out.close();
        }

        static Scanner sc = new Scanner(System.in);
        static PrintWriter out = new PrintWriter(System.out);




    //强迫症
    public static void main1(String[] args) {
        String line = new Scanner(System.in).nextLine();
        if(line.length()==4&&Integer.parseInt(line.substring(0,2))<22)
            System.out.print("20"+line.substring(0,2)+"-"+line.substring(2));
        else if(line.length()==4)
            System.out.print("19"+line.substring(0,2)+"-"+line.substring(2));
        else
            System.out.print(line.substring(0,4)+"-"+line.substring(4));
    }
}